Field of the Invention
This invention relates generally to a thermocouple probe positioned to extend into and measure the temperature of the exhaust gas flow of a gas turbine engine and, more particularly, to a thermocouple probe assembly including a thermocouple probe positioned to extend into and measure the temperature of the exhaust gas flow of a gas turbine engine, where the probe assembly includes a liner boss that secures the probe to an outer liner associated with an exhaust gas diffuser and includes a plenum pipe through which the probe extends and that seals an airflow plenum between a turbine casing and a plenum wall.
Discussion of the Related Art
The world's energy needs continue to rise which provides a demand for reliable, affordable, efficient and environmentally-compatible power generation. A gas turbine engine is one known machine that provides efficient power, and often has application for an electric generator in a power plant, or engines in an aircraft or a ship. A typical gas turbine engine includes a compressor section, a combustion section and a turbine section. The compressor section provides a compressed airflow to the combustion section where the air is mixed with a fuel, such as natural gas. The combustion section includes a plurality of circumferentially disposed combustors that receive the fuel to be mixed with the air and ignited to generate a working gas. The working gas expands through the turbine section and is directed across turbine blades therein by associated vanes. As the working gas passes through the turbine section, it causes the blades to rotate, which in turn causes a shaft to rotate, thereby providing mechanical work.
The turbine section of a typical gas turbine engine includes a plurality of rows of circumferentially disposed blades, such as four rows of blades, where the working gas is directed by a row of vanes across the blades from one stage of the blades to the next stage of the blades. At the output of the turbine section, the working gas passes through an exhaust gas diffuser that recovers the dynamic head of the exhaust gas for optimal performance of the turbine section. The exhaust gas, which is still very hot, is often times directed to other systems that may benefit from the available heat until the working gas is eventually exhausted to the environment or otherwise. For example, the hot exhaust gas at the output of the gas turbine engine may be used to boil water for a steam turbine, which also generates power in, for example, a combined cycle plant, well known to those skilled in the art. The configuration of the exhaust gas diffuser at the output of the gas turbine engine is important for the performance of the gas turbine blades because the exhaust gas diffuser partially blocks the gas flow from the turbine section.
It is necessary to provide thermocouple temperature probes, or other temperature sensing devices, that extend into the hot exhaust gas path downstream of the turbine blades to measure the temperature of the exhaust gas and ensure that the engine combustors are operating properly, where a separate thermocouple probe is generally provided for each engine combustor. For example, the temperature measured by the thermocouple probes are compared to each other to make sure that any one or more of the combustors is providing the same temperature gas as the other combustors. In order to perform properly, the thermocouple probe sensor needs to be positioned at a specific location within the hot exhaust gas flow, which often presents substantial difficulties for probe design depending on the architecture of the turbine engine. Particularly, the configuration and components of the turbine section and exhaust gas diffuser often limit packaging and access for mounting the thermocouple probe, and may require sealing around the probe to prevent airflow leaks. High temperatures inherent within the turbine section of the engine push materials to their limits and also create large thermal growth differences between casing walls and other components. Vibrations and the constant loading caused by the hot exhaust gas flow also create a considerable amount of stress and fatigue. Further, the thermocouple probe must be designed so that all thermocouple probes remain operable to continuously monitor combustor operation during an entire service interval without maintenance.
Conventional thermocouple probes for gas turbine engines are generally rigidly mounted to the turbine casing where the probe extends through a hole in the outer liner of the exhaust gas diffuser and into the hot exhaust gas path. Modern gas turbine engine designs sometimes include an air plenum for providing cooling air to various turbine section components that is located at the position where the temperature of the exhaust gas needs to be monitored. These designs often require complex static, sometimes dynamic, seals to seal the hot exhaust gas from leaking into the engine enclosure. However, these seals are highly susceptible to wear given the temperatures, vibrations and thermal movement of the casings and/or the thermocouple probe. One thermocouple probe design for these modern engines includes a long thermocouple wire fed into a tube extending out of the back of the exhaust gas diffuser. However, these types of routed designs of thermocouple probes can be vulnerable to assembly and service issues as damaged parts inside the tube cannot be easily replaced.